1. Field of the Invention
The present invention relates to radiotherapy systems, and more particularly to a radiotherapy system that can monitor a target location in real time.
2. The Prior Arts
In medical science, cancer is also called malignant neoplasm, which is a disorder in the mechanism that controls the growth of cells. Cancer has become a major cause of death in developed countries. In Taiwan, the statistics show that cancer has been the first cause of mortality for 29 years. There are multiple types of cancers, and the seriousness of the cancers depends on several factors including the location of the cancer cells, the degree of malignant growth, and the occurrence of distant metastasis. Many cancers can be treated and even cured, depending on its type, location and development stage. With respect to patients who are in locally-advanced cancers which cannot be removed by surgery ablation or who want to preserve the affected organ, radiotherapy may be an effective treatment.
Radiotherapy uses radiation to kill the cancer cells or reduce the size of the tumor cells. Radiotherapy includes external beam radiotherapy (or teletherapy) and brachytherapy. Because the cancer cells grow faster than normal cells, the application of radiation can destroy the genetic material of the cells, which can stop the growth or replication of the cells. The growth of the cancer cells thus can be restrained. However, the effect of radiotherapy is only limited to the region that receives the radiation. The goal of radiotherapy is to kill a maximum amount of cancer cells without affecting the healthy tissue. Radiotherapy may be adapted for treating solid tumor at diverse locations, such as brain, breast, uterine cervix, throat, lung, kidney, prostate, skin, stomach, uterus, or soft tissue. In certain situations, radiotherapy may also be used to treat leukemia and lymphoma. Whether the tumor and side effects are effectively controlled is based on the proper radiation dose that is applied to kill the tumor cells without significantly damaging the surrounding healthy cells.
As technology advances, the development of new imaging equipment and radiotherapy apparatuses makes possible conformal radiotherapy. Three-dimensional conformal radiotherapy uses high-energy X rays that are emitted in different fields and under different angles, so that the dose can be accumulated in space. The region of high dosage can be thereby distributed conformal to the shape of the tumor, and a mask can protect the healthy tissue surrounding the tumor. With this treatment method, the tumor receives a concentrated dosage, whereas the dosage received by the healthy tissue and important organs can be reduced. As a result, the local control rate is increased, and the occurrence of complications is reduced.
The radiation sources most frequently implemented in radiotherapy are linear accelerators that can generate curative high-energy electron or X rays that can be adjustable. A multi-leaf collimator may also be used to control the direction and shape of the radiation beam to conform with the shape of the tumor to treat. Alternatively, the radiotherapy can also use a cyclotron to generate high-energy protons for treating the tumor. Recently, several conformal radiotherapy approaches have been developed, for example intensity modulated radiotherapy and tomotherapy, which have been clinically tested as applicable methods.
Usually, there may be several weeks between the time when computed tomography images are taken from the patient for evaluating the treatment plan, and the time when radiation treatment is actually applied. Whether the shape of the tumor has changed in this time interval may be verified by test slices shot under different angles before the treatment, whereby the exactitude of the angle and field of the treatment can be confirmed. However, inadvertent displacements of the target region may happen during the treatment. These displacements may be caused by, for example, breathing movements or movements of the patient owing to discomfort or prolonged holding of a same position. If it is small, the displacement may be unperceived by the operator. As a result, the region where radiation is actually applied may be offset from the initial target, so that the tumor does not receive the prescribed radiation dose, whereas the surrounding healthy tissue may be damaged by an exposure to excessive radiation. While conformal radiotherapy has been widely accepted for treating cancer tumors, the accuracy of this method mainly relies on the computed tomography images that are usually generated in the beam's eye view. The pretreatment verification mentioned previously is also based on the same computed tomography images that are not shot in real time. Given these limitations, current radiotherapy techniques cannot ensure that the treated target is continuously in the range of the radiation beam.